Merge pull request #91 from amatsuda/index_on_yyyymm

Add index on messages#yyyymm

Author: amatsuda

db/migrate/20251220070408_add_index_to_messages_yyymm.rb

@@ -0,0 +1,5 @@
+class AddIndexToMessagesYyymm < ActiveRecord::Migration[8.1]
+  def change
+    add_index :messages, :yyyymm
+  end
+end